All of the commands, spells, or prayers that are specific to a
class are ranked by letters from A to L. These ranks help
identify about how 'potent' a command is and when, generally
speaking, you might hope to obtain it.
Your character never 'learns a rank', so a question such as 'What
rank am I?' has no real answer. Commands become available
only when you have reached the required skill level needed for
the command in the particular skill it uses. For example, if a
command is based on the attack skill, how high your level, stats,
or any other skills are won't matter.
The rank of a command gives you an idea of what range of skill
levels you might expect it to occur. Of course, what player level
you get a command will vary because your skills have different
maxes. For the main skill of your class (attack, stealth, magic,
faith or discipline), you might expect rank A commands during newbie
levels, rank B as a low mid, and rank C as a high mid, if you keep
that main skill maxed.